I haven't looked at the first reference, but in the second one they have chosen a poor example of radial to compare with.
There is really not a lot of difference between the two types, the balance is usually tilted towards axial for home construction as it can be done without a lathe.
The only thing I can think of in favour of the dual stator is that with thinner stators it may be more practical to use overlaping coils and the cooling may be better.
Having extra mechanical air gaps reduces the effective winding area.
I think they were rather worried about magnet cooling. The newer grades of Neo are better and I haven't noticed it to be a problem anyway.
Flux